This invention relates to azeotropes, azeotrope-like compositions, and methods of using azeotropes and azeotrope-like compositions to clean substrates, deposit coatings, transfer thermal energy, and as a reactant medium.
Chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), and hydrochlorocarbons (HCCs, e.g., 1,1,1-trichloroethane and carbon tetrachloride) have been used in a wide variety of solvent applications such as drying, cleaning (e.g., the removal of flux residues from printed circuit boards), and vapor degreasing. Such materials have also been used in refrigeration and heat-transfer processes. While these materials were initially believed to be environmentally benign, they have now been linked to ozone depletion. According to the Montreal Protocol and its attendant amendments, production and use of CFCs must be discontinued (see, e.g., P. S. Zurer, xe2x80x9cLooming Ban on Production of CFCs, Halons Spurs Switch to Substitutes,xe2x80x9d Chemical and Engineering News, page 12, Nov. 15, 1993). The characteristics sought in replacements, in addition to low ozone depletion potential, typically have included boiling point ranges suitable for a variety of solvent cleaning applications, low flammability, and low toxicity. Solvent replacements also should have the ability to dissolve both hydrocarbon-based and fluorocarbon-based soils. Preferably, solvent replacements will also be low in toxicity, have no flash points (as measured by ASTM D3278-89), have acceptable stability, have short atmospheric lifetimes, and have low global warming potentials.
Certain perfluorinated (PFCs) and highly fluorinated hydrofluorocarbon (HFCs) materials have been evaluated as CFC and HCFC replacements in solvent applications. While these materials are generally sufficiently chemically stable, nontoxic, and non-flammable to be used in solvent applications, PFCs tend to persist in the atmosphere, and PFCs and HFCs are generally less effective than CFCs and HCFCs for dissolving or dispersing hydrocarbon materials. Also, mixtures of PFCs or HFCs with other organic solvents tend to be better solvents and dispersants for hydrocarbons than PFCs or HFCs alone.
Hydrofluoroethers (HFEs), or highly fluorinated ethers, have also gained interest as replacements for CFCs and HCFCs. HFEs are also chemically stable, have low toxicity, are non-flammable, and are non-ozone depleting. Segregated HFEs, a subclass of HFEs having all fluorine atoms segregated on one side of and/or between the ether oxygen atom(s), generally have an additional advantage, when compared to many of their non-segregated HFE counterparts, of having very short atmospheric lifetimes (typically less than 5 years and as low as 0.77 years). However, as with PFCs and HFCs, co-solvents with hydrocarbons are desirable to improve solvency and dispersibility.
Many azeotropes possess properties that make them useful solvents. For example, azeotropes have a constant boiling point which avoids boiling temperature drift during processing and use. In addition, when an azeotrope is used as a solvent, the properties of the solvent remain constant because the composition of the solvent does not change during boiling or reflux. Azeotropes that are used as solvents also can be recovered conveniently by distillation. For relatively low boiling (boiling point below 80xc2x0 C.) segregated HFEs, such as C4F9OCH3, C4F9OC2H5 and C3F7OCH3, useful azeotropes and azeotrope-like compositions have been identified with hydrocarbon or chlorinated hydrocarbon solvents, such as paraffinic hydrocarbons, alcohols and chlorinated ethylenes. However, no azeotropes or azeotrope-like compositions have yet been identified which include higher boiling segregated HFEs. Higher boiling HFEs are particularly suitable for removing deposits which require a high temperature to soften, such as waxes, high-viscosity greases, etc., but higher boiling HFEs are generally relatively poor solvents when used alone.
Thus, there is a need for azeotrope or azeotrope-like compositions that can replace higher boiling chlorine-containing solvents such as trichloroethane, carbon tetrachloride, trichloroethylene, and perchloroethylene. Preferably, these compositions are non-flammable, have good solvency, are non-ozone depleting, and have a relatively short atmospheric lifetime so that they do not significantly contribute to global warming.
The present invention provides azeotropes and azeotrope-like compositions of a higher boiling segregated HFE. These compositions are preferably non-flammable, have good solvency, are non-ozone depleting, and have a relatively short atmospheric lifetime.
In one aspect, the present invention provides azeotrope and azeotrope-like compositions consisting essentially of a hydrofluoroether and an organic solvent. The hydrofluoroether, 3-ethoxy-perfluoro(2-methylhexane), is represented by the general formula RfCF(OC2H5)CF(CF3)2, where Rf is a straight chain perfluoroalkyl group having 3 carbon atoms. The organic solvent is selected from the group consisting of: (a) unsubstituted straight chain, branched chain, and cyclic saturated alkanes containing 8 to 11 carbon atoms; (b) chlorinated straight chain, branched chain, and cyclic saturated alkanes containing 5 to 7 carbon atoms; (c) aromatic or unsaturated cyclic halogenated or unhalogenated hydrocarbons containing 7 to 10 carbon atoms; (d) esters containing 6 carbon atoms; (e) ketones containing 6 to 7 carbon atoms; (f) glycol ethers containing 6 carbon atoms; and (g) siloxanes containing 8 carbon atoms.
While the concentrations of the hydrofluoroether and the organic solvent included in the azeotrope-like composition may vary somewhat from the concentrations found in the azeotrope formed between them, the boiling points of the azeotrope-like compositions are substantially the same as those of their corresponding azeotropes. Preferably, the azeotrope-like compositions boil at ambient pressure at temperatures that are within about 1xc2x0 C. of the temperatures at which their corresponding azeotropes boil at the same pressure. Thus, the azeotrope-like compositions of the present invention include the corresponding azeotrope.
In another aspect, the present invention provides a method of cleaning objects by contacting the object to be cleaned with one or more of the azeotrope-like compositions of this invention or the vapor of such compositions until undesirable contaminants or soils on the object are dissolved, dispersed or displaced, and rinsed away.
In yet another aspect, the present invention provides a method of coating substrates using the azeotrope-like compositions as solvents or carriers for the coating material. The process comprises the step of applying to at least a portion of at least one surface of a substrate a coating composition comprising: (a) an azeotrope-like composition; and (b) at least one coating material which is soluble or dispersible in the azeotrope-like composition. Preferably, the process further comprises the step of removing the azeotrope-like composition from the coating composition, for example, by evaporation.
The present invention also provides coating compositions comprising an azeotrope-like composition and coating material which are useful in the coating process.
In yet another aspect, the present invention provides a method of transferring thermal energy using the azeotrope-like compositions as heat-transfer fluids.
In yet another aspect, this invention provides a method for preparing a desired organic compound by reacting one or more reactants in a reaction medium consisting essentially of the azeotrope-like compositions of the present invention.